Drug interaction profile for GSK , a next generation non-nucleoside reverse transcriptase inhibitor

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1 British Journal of Clinical Pharmacology DOI:1.1111/j x Drug interaction profile for GSK , a next generation non-nucleoside reverse transcriptase inhibitor Steve Piscitelli, 1 Joseph Kim, 1 Elizabeth Gould, 1 Yu Lou, 1 Scott White, 2 Mark de Serres, 1 Mark Johnson, 1 Xiao-Jian Zhou, 3 Keith Pietropaolo 3 & Douglas Mayers 3 1 Infectious Diseases MDC, GlaxoSmithKline, Research Triangle Park, NC, 2 Infectious Diseases MDC, GlaxoSmithKline, Collegeville, PA and 3 Clinical Pharmacology & Early Medical Development, Idenix Pharmaceuticals Inc, Cambridge, MA, USA WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT In healthy subjects, GSK was shown to be safe and well tolerated with single doses up to 12 mg once daily and with multiple doses up to 8 mg once daily for 7 days. Furthermore, a phase IIa monotherapy study demonstrated that GSK to 8 mg once daily for 7 days was well tolerated in HIV-1 infected subjects and that doses 1 mg once daily were associated with antiviral activity (~1.8 log 1 copies ml -1 ). However, the potential for drug interactions with co-administration of GSK and other antiretroviral medications or supportive medications is not known. WHAT THIS STUDY ADDS These studies indicate that GSK was safe and well tolerated in healthy adults treated in these studies at the doses and duration of therapy evaluated. In addition, these studies indicate that few dosage modifications would be necessary if GSK were to be administered with most antiretroviral therapies or supportive medications. Correspondence Dr Steve Piscitelli, PharmD, GlaxoSmithKline, 5 Moore Drive, Research Triangle Park, NC 2779, USA. Tel.: Fax: stephen.c.piscitelli@gsk.com These data were presented in part at the 17th International AIDS Conference, Mexico City, Mexico, August 28, the 5th Interscience Conference on Antimicrobial Agents and Chemotherapy Meeting, Boston, MA, September 21, the 18th Conference on Retroviruses and Opportunistic Infections, Boston, MA, February March 211 and the 12th International Workshop on Clinical Pharmacology of HIV Therapy, Miami, FL, April Keywords antiretroviral therapy, drug-drug interaction, HIV-1 infection, NNRTI Received 16 November 211 Accepted 15 January 212 Accepted Article Published Online 3 January 212 AIM To evaluate potential drug interactions with antiretroviral therapies or supportive therapies for use in conjunction with the once daily, next generation non-nucleoside reverse transcriptase inhibitor GSK in patients with HIV-1 infection. METHODS A series of phase I drug interaction studies was conducted. RESULTS GSK was shown to be a weak CYP3A4 and CYP2D6 inhibitor in a clinical study with a probe cocktail. Mean plasma concentration time profiles for atazanavir, tenofovir disoproxil fumarate/emtricitabine (TDF/FTC), darunavir (DRV, administered with ritonavir [RTV]), and drospirenone/ethinylestradiol were similar following co-administration of GSK Plasma raltegravir AUC(,t) and C max increased by 18% with no change in Ct when raltegravir was co-administered with GSK Lopinavir (LPV) plasma AUC(,t), C max and Ct decreased by 23%, 14% and 4%, respectively, following administration of lopinavir/ritonavir with GSK Atorvastatin, rosuvastatin and simvastatin AUC(, ) and C max increased following co-administration with GSK , with the largest changes observed for simvastatin (3.7-fold and 4.3-fold). Changes in maximum and extent of GSK exposure were marginal after co-administration with atazanavir, TDF/FTC and raltegravir compared with GSK administered alone. Co-administration of GSK with DRV/RTV and LPV/RTV increased plasma GSK exposures by to 2-fold compared with GSK administered alone, and increases in GSK exposure were higher following single dose co-administration of DRV/RTV or LPV/RTV compared with multiple doses. There were few drug-related AEs, and no treatment-related trends in blood chemistry, haematology, urinalysis, vital signs or ECG findings. CONCLUSIONS These studies indicate that GSK was safe and well tolerated in healthy adults treated in these studies at the doses and duration of therapy evaluated. 336 / Br J Clin Pharmacol / 74:2 / ViiV Healthcare British Journal of Clinical Pharmacology 212 The British Pharmacological Society

2 Drug interaction profile of GSK Introduction GSK is a once daily, next generation nonnucleoside reverse transcriptase inhibitor (NNRTI). In vitro data indicated GSK has a different resistance profile from efavirenz and is active against efavirenzresistant viruses [1]. After GSK was shown to be safe and well tolerated with single doses up to 12 mg once daily and with multiple doses up to 8 mg once daily for 7 days in healthy subjects [2], phase IIa monotherapy studies were initiated to investigate the safety and short term efficacy of GSK in HIV-1 infected subjects. These studies demonstrated that GSK to 8 mg once daily for 7 days was well tolerated in HIV-1 infected subjects [3]. In addition, GSK in doses of 1 mg once daily or greater achieved mean reductions in viral load of approximately 1.8 log 1 copies ml -1, and a pharmacokinetic/pharmacodynamic (PK/PD) relationship was identified and characterized. Furthermore, no NNRTI resistance mutations were selected during 7 days of monotherapy with GSK [4]. Although phase IIb trials of GSK have since been placed on clinical hold after five reports of seizures in treatment-experienced patients, a series of phase I studies was initially designed to study the safety and potential for drug interactions with co-administration of GSK and other antiretroviral medications or supportive medications. In vitro studies suggested GSK inhibited human cytochrome P45 (CYP45) enzymes 2C8, 2C9, and 2C19, as well as human organic anion transport protein (OATP1B1 and OATP1B3) [2, 5, 6]. In addition, GSK demonstrated weak 2D6 and 3A4 inhibition in a clinical study with a probe cocktail [5]. As such, one of the goals of these studies was to examine if GSK interacts with CYP45 or OATP1B1 substrates (e.g. boosted protease inhibitors, statins).these studies also aimed to examine the potential for two-way interactions between drugs likely to be used in combination with GSK to treat HIV infection. Methods Study designs A series of phase I trials was conducted between October 27 and February 211 (Table 1). Subject eligibility was assessed by physical examination, medical history and laboratory testing. Healthy adult males and females of non-childbearing potential were enrolled in all studies except for the oral contraceptive study, which only enrolled female subjects. Subjects were excluded for a positive HIV or hepatitis C antibody or a positive hepatitis B surface antigen. Subjects were not allowed to receive any prescription or non-prescription drugs, including vitamins or herbal supplements, within 7 days before the first dose and throughout the study. Subjects had a screening visit within 3 days before the first dose of the study drug and a follow-up visit after the last dose of the study drug. Written informed consent was obtained from all subjects, and the protocol and any amendments were approved by institutional review boards. Assessments Safety assessments included monitoring of adverse events (AEs), serious adverse events (SAEs), and concomitant medications, as well as regular checks of clinical chemistry, haematology, urinalysis, vital signs and electrocardiogram (ECG) readings. Serial blood samples for determination of plasma concentrations were collected at appropriate intervals during each study (Table 2). After extraction from plasma by protein precipitation, concentrations of GSK and concomitant medications were determined by validated, high performance liquid chromatography tandem mass spectrometry methods. Noncompartmental PK analyses of concentration time data were performed with WinNonlin (Pharsight Corporation, St Louis, MO). Parameters included area under the concentration time curve (AUC), minimum observed plasma concentration (C min), maximum observed plasma concentration (C max), time of occurrence of C max (t max), concentration at end of dosing interval at steady-state (Ct), apparent oral clearance (CL/F), and apparent terminal elimination phase half-life (t 1/2). AUC was calculated using the linear-up/log-down trapezoidal method. Statistical analyses Statistical analyses were performed on the logtransformed PK parameters, AUC(,t), Ct and C max. Analysis of variance was performed using the SAS mixed linear models procedure. The ratio of geometric least squares (GLS) means and associated 9% confidence interval (CI) was estimated for the PK parameters of interest. Results Drug interactions with antiretroviral therapies Atazanavir The mean plasma atazanavir (ATV) concentration time profiles were similar on day 7 after co-administration of GSK mg or 8 mg with ATV 1 mg (Figure 1). The mean ATV C max and AUC(,t) were 128% to 144% and 111% to 161%, respectively, with GSK compared with ATV 1 mg alone (Table 3). As expected, ATV concentrations were substantially higher after co-administration of ritonavir (RTV) 1 mg and 1 mg ATV (Figure 1). A single dose design with a low dose of ATV was primarily selected to limit exposure to ATV in healthy volunteers since ATV is an inhibitor of UDPglucuronyl transferase (UGT) and is associated with increases in unconjugated bilirubin and occasional jaundice [7]. Also, the potential boosting effect of GSK on ATV is unknown. As such, the extent of exposure after Br J Clin Pharmacol / 74:2 / 337

3 S. Piscitelli et al. Table 1 Study designs Study identifiers Trial design Subjects enrolled, N Description of treatment groups NV-5A-3 NV-5A-4 NCT9288; SGN11345 NCT111893; SGN NCT113872; SGN NCT ; SGN Phase I, randomized, open-label, two period, parallel-group study Phase I, randomized, placebo-controlled, two step, parallel-group study Phase I, open-label, three-period study Phase I, open-label, three period, fixed-sequence crossover study Phase I, open-label, single-sequence study Phase I, randomized, two period, double-blind crossover study 18 Group A: ATV 1 mg (day 1), washout (days 2 5), GSK mg (day 6), GSK mg + ATV 1 mg (day 7) Group B: ATV 1 mg (day 1), washout (days 2 5), GSK mg (day 6), GSK mg + ATV 1 mg (day 7) Group C: ATV 1 mg (day 1), washout (days 2 5), RTV 1 mg (day 6), RTV 1 mg + ATV 1 mg (day 7) 28 Group A: TDF/FTC (TDF 3 mg + FTC 2 mg) once daily on days 1 14, GSK mg once daily on days 8 14 Group B: GSK matching placebo* once daily on days 1 7, GSK mg once daily on days 8 14 Group C: Control placebo* once daily on days 1 7, GSK mg once daily on days Cohort 1: Midazolam 3 mg + dextromethorphan 3 mg (day -2), flurbiprofen 5 mg (day -1), GSK mg once daily (days 1 11), GSK mg + midazolam 3 mg + dextromethorphan 3 mg (day 12), GSK mg + flurbiprofen 5 mg (day 13), GSK mg + LPV/RTV 4/1 mg (day 14), washout (days 15 21), LPV/RTV 4/1 mg twice daily (days 22 28), GSK once daily + LPV/RTV 4/1 mg twice daily (days 29 35) Cohort 2: GSK mg once daily (days 1 13), GSK mg + DRV/RTV 6/1 mg (day 14), washout (days 15 21), DRV/RTV 6/1 mg twice daily (days 22 28), GSK once daily + DRV/RTV 6/1 mg twice daily (days 29 35) 15 Period 1: RAL 4 mg twice daily for 5 days followed by a washout period of 5 days Period 2: GSK mg once daily for 5 days Period 3: RAL 4 mg twice daily + GSK mg once daily for 5 days 14 Simvastatin 2 mg (day 1), washout (day 2), atorvastatin 2 mg (day 3), washout (days 4 6), rosuvastatin 1 mg (day 7), washout (days 8 9), GSK mg once daily (days 1 14), GSK mg + simvastatin 2 mg (day 15), GSK mg once daily (days 16 17), GSK mg + atorvastatin 2 mg (day 18), GSK mg once daily (days 19 21), GSK mg + rosuvastatin 1 mg (day 22), GSK mg once daily (days 23 24) 1 Group 1: Ethinylestradiol/drospirenone + GSK mg once daily (days 1 11), ethinylestradiol/drospirenone + placebo once daily (days 12 21) Group 2: Ethinylestradiol/drospirenone + placebo once daily (days 1 11), ethinylestradiol/drospirenone + GSK mg once daily (days 12 21) ATV, atazanavir; DRV, darunavir; FTC, emtricitabine; LPV, lopinavir; RAL, raltegravir; RTV, ritonavir; TDF, tenofovir disoproxil fumarate. *GSK matching placebo capsules contained Gelucire 44/14 (Gattefossé, Saint-Priest, Lyon, France) while control placebo capsules contained microcrystalline cellulose to allow for assessment of potential interactions of GSK and/or vehicle with thyroid function tests. GSK dose was determined during period 1 (i.e. days 1 14). Subjects who were not already on a stable regimen of ethinylestradiol/drospirenone were required to switch to ethinylestradiol/drospirenone for at least 21 days to evaluate tolerability, followed by a washout period of 7 days, before continuing to treatment periods. Due to the early termination of the study, only 1 subjects completed the study and were included in the pharmacokinetic population. administration of ATV alone was difficult to estimate and Ct could not be determined for most treatment groups. After administration of GSK (1 mg or 8 mg) and ATV 1 mg, increases in peak mean GSK concentrations were observed compared with GSK administered alone. Co-administration of GSK mg and 8 mg with ATV resulted in increases in plasma GSK exposures with AUC(,t), C max and Ct of 65% to 68%, 4% to 26%, and 115% to 236%, respectively (Table 3). Two subjects (11%) had AEs determined to be potentially related to ATV (one subject with both headache and nausea) and GSK (headache in one subject). All AEs were mild and transient. No SAEs or deaths were reported and no subject withdrew from the study due to an AE. With the exception of increased mean bilirubin values observed post-study for three subjects in group C (i.e. the group receiving ATV/RTV), there did not appear to be any important treatment-related trends for any laboratory parameter. In addition, there were no clinically significant trends in vital signs or ECG readings during study drug dosing. Tenofovir disoproxil fumarate and emtricitabine Mean plasma concentrations of tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) were not significantly altered by co-administration with GSK compared with TDF/FTC (Gilead Sciences, Inc, Foster City, CA) administered alone (Figure 2A and B). In addition, all plasma TDF and FTC PK parameters were comparable after co-administration of TDF/FTC and GSK relative to administration of TDF/FTC alone. No interactions were observed between TDF/FTC and GSK with respect to maximum (C max) and extent (AUC at steady state, AUC ss) of TDF (mean ratios of 114% and 16%, respectively) or FTC exposure (mean ratios of 96% and 16%, respectively). A lower maximum (mean ratio of 83%) and extent (mean ratio of 8%) of GSK exposure were 338 / 74:2 / Br J Clin Pharmacol

4 Drug interaction profile of GSK Table 2 Schedule of blood sampling for plasma concentrations Drug interaction study Timing of pharmacokinetic sampling (days) GSK atazanavir Atazanavir: 1, 2, 7 and 8* GSK : 6, 7 and 8* GSK TDF/FTC Group A TDF/FTC: 1, 4 8 and GSK : 1, 8, and 16* Groups B/C Placebo: 1 7 GSK : 8 14 GSK boosted protease inhibitors Cohort 1 Probes: -2, -1, 12 and 13 GSK : 7, 14 and Lopinavir/Ritonavir: 14 and Cohort 2 GSK : 1 14 and Darunavir/Ritonavir: 14 and GSK raltegravir Period 1: 2 5 Period 2: 2 5 Period 3: 1 6 GSK statins 1 5, 7 9 and GSK oral 8 11 and contraceptives FTC, emtricitabine; TDF, tenofovir disoproxil fumarate. *Or early termination. Atazanavir plasma concentration (ng ml -1 ) 1 1 Figure Time (h) Mean plasma concentration vs. time on day 7 for atazanavir (ATV) 1 mg, ATV 1 mg + ritonavir (RTV) 1 mg, ATV 1 mg + GSK mg and ATV 1 mg + GSK mg. ATV ( ); ATV + RTV (1 mg) ( ); ATV + GSK (1 mg) ( ); ATV + GSK (8 mg) ( ) observed after co-administration of GSK and TDF/ FTC compared with GSK alone. Although the 9% confidence intervals of the ratio of the geometric means for GSK C max and AUC ss were not completely contained within the predefined critical range, the 9% confidence intervals were wide, indicating low precision for this comparison. The variability associated with GSK exposure was unexpectedly high due in part to one subject in group C whose exposure was approximately 2- to 3-fold higher compared with the median values for AUC(,t) and C max (there was an approximately 2% lower maximum and overall extent of GSK exposure after administration of GSK and TDF/FTC compared with GSK alone). Seventy-six AEs were reported, most occurring before exposure to GSK (79%).The most common AE was headache (reported by 25% of subjects). The majority of AEs were mild (82%) and there were no SAEs or deaths in the study. Three subjects discontinued because of AEs before exposure to GSK (two for rash/pruritus and vomiting possibly related to TDF/FTC and one because of an infected insect bite requiring concomitant medications). There were no treatment-related trends in blood chemistry, haematology, urinalysis, vital signs or ECG findings. Although GSK could affect thyroid function, most thyroid function variables remained within normal limits, and no subjects experienced clinically significant abnormal values for any thyroid function parameter. Raltegravir Co-administration of GSK mg once daily and raltegravir (RAL) 4 mg twice daily did not result in clinically significant PK interactions (Figure 3). A decrease in plasma RAL AUC(,t) and C max of 18% (9% CI of.555, 1.2 and.482, 1.38, respectively) and no change in Ct were observed when RAL 4 mg twice daily was co-administered with GSK mg once daily (Table 4). Co-administration of RAL with GSK resulted in mean increases in plasma GSK AUC(,t), C max and Ct of 15%, 16% and 13%, respectively (Table 4). The most frequently reported AE was nausea, occurring in three subjects receiving GSK alone (only one instance was determined to be drug related). All AEs were mild. There were no SAEs or deaths reported and no subjects discontinued the study due to an AE. In addition, there were no clinically significant changes in vital signs or ECG findings, and no clinical laboratory values were reported during the study as AEs. CYP45 probes and boosted protease inhibitors Coadministration of metabolic probes with repeat doses of GSK mg resulted in increases in midazolam and dextromethorphan AUC(, ) of 54% and 83%, respectively. No changes were observed in plasma flurbiprofen AUC(, ) or in the 4-OH flurbiprofen AUC(,24 h) : flurbiprofen AUC(,24 h) ratio (i.e. metabolite : parent compound ratio). When darunavir/ritonavir (DRV/RTV) 6/1 mg twice daily was administered with GSK mg once daily, there were no effects on DRV pharmacokinetics (decreases in maximum and extent of DRV exposure of 5%) or on plasma RTV exposure (increases in maximum and extent of RTV exposure of 2%). However, co-administration of lopinavir/ritonavir (LPV/RTV) 4/1 mg twice daily with GSK mg once daily was associated with decreases in plasma LPV AUC(,t), C max and Ct (23%, 14% Br J Clin Pharmacol / 74:2 / 339

5 S. Piscitelli et al. Table 3 Summary of treatment comparisons for GSK and atazanavir Plasma parameter GSK mg + ATV vs. ATV ATV GSK mg + ATV vs. ATV GLS mean ratio (9% CI) RTV 1 mg + ATV 1 mg vs. ATV GSK mg + ATV vs. GSK GSK GSK mg + ATV vs. GSK AUC(,t) 1.11 (.8, 1.54) 1.61 (1.7, 2.41) (17.87, 37.5) 1.65 (1.42, 1.91) 1.68 (1.31, 2.14) C max 1.28 (.87, 1.88) 1.44 (.92, 2.27) (11.55, 19.96) 1.4 (.97, 1.12) 1.26 (1.9, 1.45) Ct 3.36 (2.34, 4.82) 2.15 (1.68, 2.77) ATV, atazanavir; AUC(,t), area under the concentration time curve; CI, confidence interval; C max, maximum observed plasma concentration; Ct, concentration at end of dosing interval at steady state; GLS, geometric least squares; RTV, ritonavir. A Mean TDF concentration (ng ml -1 ) B Mean FTC concentration (ng ml -1 ) , 1 1 Figure 2 Time (h) Time (h) Mean plasma concentration vs. time on day 14 for (A) tenofovir disoproxil fumarate (TDF) and (B) emtricitabine (FTC) each alone and with GSK (A) TDF ( ); TDF + GSK ( ). (B) FTC ( ); FTC + GSK ( ) and 4%,respectively),while plasma RTV AUC(,t),C max and Ct were decreased by 19%, 21% and 42%, respectively. Co-administration of single and repeat doses of DRV/ RTV or LPV/RTV with GSK increased plasma GSK exposures compared with GSK administered alone (Table 5). In general, the increases in plasma GSK exposure were less than 2-fold, and GSK exposure increased more with single dose co-administration of LPV/RTV or DRV/RTV than with co-administration of repeat doses of LPV/RTV or DRV/RTV. Overall, 11 subjects (46%) experienced drug-related AEs. All drug-related AEs were mild to moderate, with diarrhoea, somnolence and headache being the most common. Three subjects withdrew from the study due to AEs, one of which was possibly related to the study drug (GSK LPV/RTV). There were no clinically significant changes in laboratory tests, vital signs or ECG parameters. Drug interactions with supportive medications Statins Mean plasma concentrations of select statins and statin metabolites when statins were administered alone or with GSK are presented in Figure 4. Co-administration of GSK mg once daily with a single dose of atorvastatin 2 mg or rosuvastatin 1 mg increased AUC(, ) and C max by approximately 4% and 3%, respectively, relative to either statin alone (Table 6). However, the increase in atorvastatin PK parameters was offset by commensurate decreases in ortho-hydroxy atorvastatin PK parameters. Simvastatin AUC(, ) and C max increased 3.7-fold and 4.3-fold, respectively, after co-administration of simvastatin with GSK relative to simvastatin alone. Two subjects experienced mild drug-related AEs, but there were no SAEs, deaths or withdrawals due to AEs. In addition, there were no treatment-related laboratory findings or clinically significant changes in vital signs or ECG readings. Oral contraceptives Ten subjects completed the study and were included in the PK summary population. In those subjects, an increase in plasma drospirenone AUC(,t), C max and C min of 18% to 22% was observed when ethinylestradiol/drospirenone (Bayer HealthCare Pharmaceuticals, Inc, Leverkusen, Germany) was co-administered with GSK , whereas no changes in plasma 34 / 74:2 / Br J Clin Pharmacol

6 Drug interaction profile of GSK A 3.5 Linear scale 1 Semilogarithmic scale Concentration (µg ml -1 ) Concentration (µg ml -1 ) Planned relative time (h) Planned relative time (h) B 2.5 Linear scale 1 Semilogarithmic scale Concentration (µg ml -1 ) Concentration (µg ml -1 ) Planned relative time (h) Planned relative time (h) 24 Figure 3 Mean plasma concentration vs. time for (A) GSK mg once daily alone and with raltegravir (RAL) 4 mg twice daily and (B) raltegravir 4 mg twice daily alone and with GSK mg once daily. (A) GSK ( ); GSK RAL ( ). (B) RAL ( ); GSK RAL ( ) Table 4 Plasma GSK and raltegravir pharmacokinetic treatment comparisons Pharmacokinetic parameter GSK GLS mean ratio (9% CI) GSK raltegravir vs. GSK Raltegravir GLS mean ratio (9% CI) GSK raltegravir vs. raltegravir AUC(,t) 1.15 (1.4, 1.26).82 (.56, 1.2) C max 1.16 (1.5, 1.28).82 (.48, 1.38) Ct 1.13 (1.3, 1.25) 1.4 (.82, 1.32) AUC(,t), area under the concentration time curve; CI, confidence interval; C max, maximum observed plasma concentration; Ct, concentration at end of dosing interval at steady state; GLS, geometric least squares. ethinylestradiol AUC(,t) and C max were observed. Furthermore, no differences in maximum luteinizing hormone or follicle-stimulating hormone concentrations between the two treatments were observed. Three AEs were considered drug related (one report of headache in both the ethinylestradiol/drospirenone + GSK and the ethinylestradiol/drospirenone alone groups and one report of upper abdominal pain in the Br J Clin Pharmacol / 74:2 / 341

7 S. Piscitelli et al. Table 5 Plasma GSK pharmacokinetic treatment comparisons Pharmacokinetic parameter Cohort 1 Cohort 2 GLS mean ratio (9% CI) GLS mean ratio (9% CI) GSK LPV/RTV SD vs. GSK GSK LPV/RTV RD vs. GSK GSK DRV/RTV SD vs. GSK GSK DRV/RTV RD vs. GSK AUC(,t) 1.97 (1.62, 2.4) 1.25 (1., 1.56) 1.93 (1.66, 2.24) 1.41 (1.7, 1.86) C max 1.43 (1.14, 1.8) 1.23 (1.3, 1.47) 1.5 (1.3, 1.74) 1.34 (1.12, 1.6) Ct.97 (.85, 1.11) 1.61 (1.9, 2.39) 1.1 (1., 1.2) 1.58 (1.9, 2.29) AUC(,t), area under the concentration time curve; CI, confidence interval; C max, maximum observed plasma concentration; Ct, concentration at end of dosing interval at steady state; DRV, darunavir; GLS, geometric least squares; LPV, lopinavir; RD, repeat dose; RTV, ritonavir; SD, single dose. ethinylestradiol/drospirenone alone group).there were no SAEs, withdrawals due to AEs or deaths. All AEs were mild to moderate, except one instance of severe diarrhoea in a patient receiving ethinylestradiol/drospirenone alone (resolved in ~24 h, not considered treatment related). There were no grade 3 or 4 treatment-emergent laboratory values and no clinically significant vital sign values or ECG abnormalities were observed. Discussion This series of drug interaction studies evaluated the potential for interactions between GSK (up to 8 mg) and a variety of antiretroviral therapies and supportive medications in healthy adult subjects. A marginal drug interaction effect was noted on ATV PK after administration of GSK , with mean ratios of C max and AUC(,t) indicating an 11% to 61% higher maximum and overall extent of ATV exposure following combination therapy compared with administration of ATV 1 mg alone. There was a moderate, but not likely to be clinically meaningful, drug interaction effect on the overall extent of GSK exposure [percent mean ratio for AUC(,t) of 165% 168%] and minimum GSK concentrations (percent mean ratio for Ct of 215% 336%) after co-administration of ATV with either GSK mg or 8 mg. By contrast, ATV had only a slight effect on the maximum exposure of GSK mg or 8 mg. Available data suggest that GSK is primarily metabolized through oxidation and to a lesser extent through conjugation (e.g. glucuronidation). Thus, the increase in GSK exposure is likely attributable to the inhibitive effects of ATV on both CYP45 3A and UGT1A1 [8, 9]. There was no drug interaction between GSK and TDF/FTC with respect to TDF and FTC. However, this study may not have been adequately powered to assess conclusively drug interaction with respect to GSK because of the high variability of PK parameters for GSK In addition, the higher median C max and AUC(,t) noted for one subject in group C may have skewed the data towards an indication of a drug interaction. Regardless, the data indicated no apparent dose or exposure response relationship within the dose range covered in this study, suggesting the marginal change in exposure was unlikely to be clinically relevant. As RAL does not inhibit CYP3A or UGT1A1, RAL was not expected to alter plasma GSK exposure, and the marginal increases in plasma GSK exposure observed when GSK was co-administered with RAL were not clinically significant. Since RAL is eliminated through UGT1A1 metabolism and GSK had been demonstrated to inhibit UGT1A1 in vitro (IC 5 = 2.8 mm;data not shown), it was possible that co-administration of GSK could increase RAL exposure. Consistent with many drug-drug studies, RAL was associated with large intersubject variability (i.e. 9% CIs of the geometric least square mean ratios for PK parameters were wide). However, the changes observed in RAL PK when co-administered with GSK were not clinically significant. Thus, no RAL dosage adjustments are required when RAL is co-administered with GSK The increases in midazolam and dextromethorphan AUC(,t) of 5% to 8% when each was co-administered with GSK indicate that GSK is a weak CYP3A4 and CYP2D6 inhibitor, while the lack of effect of flurbiprofen suggests GSK does not affect CYP2C9 activity.these data confirm the findings of the phase I trial with ATV and suggest GSK has low drug interaction potential when co-administered with other drugs that are primarily metabolized through CYP45. Given that midazolam, DRV and LPV are all predominantly metabolized by CYP3A4, the decrease in LPV exposure is inconsistent with the increased midazolam exposure and lack of change in the DRV/RTV exposure. At this time, the mechanism involved in the reduced LPV/RTV concentrations observed with GSK co-administration is unknown, and the clinical significance of this interaction remains to be determined. The greater increase in exposure of GSK after a single dose than after repeated doses may have occurred because the inhibition of CYP3A4 or other enzymes/transporters was counteracted by 342 / 74:2 / Br J Clin Pharmacol

8 Drug interaction profile of GSK A Simvastatin plasma concentration (ng ml -1 ) Time post dose (h) Simvastatin acid plasma concentration (ng ml -1 ) Time post dose (h) B Atorvastatin plasma concentration (ng ml -1 ) Time post dose (h) Ortho-hydroxy atorvastatin plasma concentration (ng ml -1 ) Time post dose (h) C 16 Rosuvastatin plasma concentration (ng ml -1 ) Time post dose (h) Figure 4 Mean plasma concentration vs.time for (A) simvastatin and simvastatin acid,(b) atorvastatin and ortho-hydroxy atorvastatin (inset of first 12 h post dose) and (C) rosuvastatin each alone and with GSK (A) Simvastatin ( ); Simvastatin + GSK ( ). (B) Atorvastatin ( ); Atorvastatin + GSK ( ). (C) Rosuvastatin ( ); Rosuvastatin + GSK ( ) Br J Clin Pharmacol / 74:2 / 343

9 S. Piscitelli et al. Table 6 Summary of effects of GSK on pharmacokinetics of select statins Analyte (treatment comparison) GLS mean ratio (9% CI) AUC(, ) AUC(,48 h) C max t 1/2 Simvastatin (D vs. A) 3.73 (2.89, 4.82) 3.74 (2.91, 4.82) 4.33 (3.7, 6.1) 1.15 (.88, 1.51) Simvastatin acid (D vs. A) 2.51 (1.89, 3.34) 2.95 (2.43, 3.58) 3.9 (3.12, 4.88).74 (.59,.92) Atorvastatin (E vs. B) 1.5 (1.29, 1.75) 1.47 (1.26, 1.7) 1.25 (.91, 1.72) 1.22 (1.1, 1.47) Ortho-hydroxy atorvastatin (E vs. B).83 (.75,.91).76 (.68,.84).41 (.3,.55) 1.69 (1.43, 1.99) Rosuvastatin (F vs. C) 1.35 (1.22, 1.48) 1.26 (1.15, 1.39) 1.32 (1.2, 1.45) 1.59 (1.32, 1.91) AUC(,t), area under the concentration time curve; CI, confidence interval; C max, maximum observed plasma concentration; GLS, geometric least squares; t1/ 2, terminal elimination phase half-life. Treatment A: simvastatin 2 mg (single dose). Treatment B: atorvastatin 2 mg (single dose). Treatment C: rosuvastatin 1 mg (single dose). Treatment D: GSK mg once daily + simvastatin 2 mg (single dose). Treatment E: GSK mg once daily + atorvastatin 2 mg (single dose). Treatment F: GSK mg once daily + rosuvastatin 1 mg (single dose). induction of these enzymes/transporters after repeat dosing.these increases in GSK are not considered clinically significant because GSK doses up to 8 mg once daily have been administered to HIV-infected subjects without clinically significant drug-related side effects. Thus, no GSK dosage adjustments are required when co-administered with DRV/RTV or LPV/RTV. Several antiretroviral agents that affect CYP3A4 are known to influence statin exposure. Efavirenz, a mixed inducer/inhibitor of CYP3A4, was associated with 4% reductions in atorvastatin, pravastatin and simvastatin exposure [1], while protease inhibitor boosters, such as ritonavir and saquinavir, have been shown to increase exposure of atorvastatin by 79% and simvastatin by up to 3% [11]. Due to the magnitude of potential inhibition of simvastatin metabolism (and the resultant risk for rhabdomyolysis), drugs that inhibit CYP3A4 are not recommended for co-administration with simvastatin [12]. In these studies, co-administration of GSK with atorvastatin, rosuvastatin and simvastatin was shown to increase significantly the exposure of these statins. Simvastatin was the most sensitive to inhibition by GSK , consistent with trends noted for other antiretroviral therapies that inhibit CYP3A4. The net atorvastatin-related inhibition by GSK was minimal as the increases in atorvastatin exposure were potentially offset by decreases in exposure of orthohydroxy atorvastatin, the CYP3A4 mediated active metabolite of atorvastatin. Exposures of rosuvastatin were increased by 26% to 32% after co-administration with GSK relative to rosuvastatin alone.therefore, atorvastatin and rosuvastatin would be preferable to simvastatin for the treatment of hyperlipidaemia in patients receiving GSK for HIV-1 infection, and monitoring of AEs related to increases in any HMG-CoA reductase inhibitor (e.g. rhabdomyolysis) is warranted. Although the oral contraceptive study evaluated a lower number of patients than originally planned because of the early study termination, there were no changes in PK of ethinylestradiol when co-administered with GSK Increases in drospirenone plasma AUC(,t) and C max when ethinylestradiol/drospirenone was co-administered with GSK (~18%) were not considered to be clinically meaningful or to require dose modification. Furthermore, changes in hormonal markers in this limited population were minimal. Although the development of GSK has been placed on clinical hold, these studies demonstrate that GSK was safe and well tolerated in healthy adults at the doses and duration of therapy evaluated. In addition, these studies indicate that few dosage modifications would be necessary if GSK were to be administered with most antiretroviral therapies or supportive medications (Table 7). Competing Interests All authors are employed by and may receive company stock as part of their incentive packages from either Glaxo- SmithKline (de Serres, Gould, Johnson, Kim, Lou, Piscitelli and White) or Idenix Pharmaceuticals, Inc (Pietropaolo, Mayers and Zhou). All listed authors meet the criteria for authorship set forth by the International Committee for Medical Journal Editors. The authors would like to acknowledge the following principal investigators and Clinical Research Unit Staff: Robert A. Blum, PharmD, Buffalo Clinical Research Center; Gregory M. Haugen, MD, Cetero Research, Azra Hussaini, MD, Parexel Baltimore Early Phase Clinical Unit, Matthew M. Medlock, MD, PPD Development and Grant Generaux, Michael Leonard, and Lindsey Webster, Preclinical Drug Metabolism and Pharmacokinetics, GlaxoSmithKline. The authors also wish to acknowledge the following individual for his editorial assistance during the development of this manuscript: Todd Parker. Funding for these studies was provided by GlaxoSmith- Kline Pharmaceuticals, LLC and ViiV Healthcare. 344 / 74:2 / Br J Clin Pharmacol

10 Drug interaction profile of GSK Table 7 Overview of dosing recommendations Drug interaction study GSK atazanavir GSK TDF/FTC GSK raltegravir GSK boosted protease inhibitors GSK statins (atorvastatin, rosuvastatin and simvastatin) GSK oral contraceptives REFERENCES Dosing recommendation(s) No GSK dosage adjustments are necessary when GSK is co-administered with atazanavir No dosage adjustments are necessary for TDF/FTC or GSK when co-administered No dosage adjustments are necessary for raltegravir or GSK when co-administered No GSK dosage adjustments are necessary when GSK is co-administered with DRV/RTV or LPV/RTV No DRV/RTV dosage adjustments are necessary when GSK is co-administered with DRV/RTV Potential interactions of LPV/RTV with GSK require further study before LPV/RTV dosage recommendations can be provided GSK should be used with caution with simvastatin doses >4 mg No dosage adjustments are necessary for ethinylestradiol/drospirenone when co-administered with GSK DRV, darunavir; FTC, emtricitabine; LPV, lopinavir; RTV, ritonavir; TDF, tenofovir disoproxil fumarate. 1 Richman DD, Jakubik J, Chapron C, Hubbard L, Gray L, Seifer M, Standring DN. Genotypic resistance and phenotypic cross-resistance profile in vitro for a novel NNRTI: IDX Poster presented at: 15th Conference on Retroviruses and Opportunistic Infections; February 3-6, 28; Boston, MA. 2 Zhou X-J, Pietropaolo K, Damphousse D, Belanger B, Chen J, Sullivan-Bólyai J, Mayers D. Single-dose escalation and multiple-dose safety, tolerability, and pharmacokinetics of IDX899, a candidate human immunodeficiency virus type 1 nonnucleoside reverse transcriptase inhibitor, in healthy subjects. Antimicrob Agents Chemother 29; 53: White S, Lou Y, Dumont E, Zala C, Zhou X-J, Kim J. Safety, efficacy, pharmacokinetic (PK), and PK/pharmacodynamics (PK/PD) of GSK , a next generation NNRTI, administered as short-term monotherapy in therapy-naïve HIV-1 infected (NV) subjects. 21. Poster presented at: 5th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy; September 12-15, 21; Boston, MA. 4 St Clair M, Dudas K, Lou Y, Zala C, Mayers D, Dumont E. GSK , an NNRTI with activity against common NNRTI resistance mutants, did not select for NNRTI resistance mutations in two seven-day monotherapy studies. 21. Slides presented at: 5th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy; September 12-15, 21; Boston, MA. 5 Ford SL, Kim J, Yu L, Gould E, White S, Piscitelli S, Johnson MA. Inhibition potential for GSK , a next-generation NNRTI, on HMG-CoA reductase inhibitors simvastatin, atorvastatin and rosuvastatin Poster presented at: 12th International Workshop on Clinical Pharmacology of HIV Therapy; April 13-15, 211; Miami, FL. 6 Richman D, Dousson C, Storer R, Moussa A, Randall J, Bridges E, Liuzzi M, Jakubik J, Seifer M, Standring D. IDX12899 and IDX12989, novel NNRTI with potent anti-hiv activity, enhanced barrier to resistance and favorable pharmacokinetic profile. 27. Presented at: 14th Conference on Retroviruses and Opportunistic Infections; February 25-28, 27; Los Angeles, CA. 7 von Hentig N. Atazanavir/ritonavir: a review of its use in HIV therapy. Drugs Today (Barc) 28; 44: Le Tiec C, Barrail A, Goujard C, Taburet AM. Clinical pharmacokinetics and summary of efficacy and tolerability of atazanavir. Clin Pharmacokinet 25; 44: Zhang D, Chando TJ, Everett DW, Patten CJ, Dehal SS, Humphreys WG. In vitro inhibition of UDP glucuronosyltransferases by atazanavir and other HIV protease inhibitors and the relationship of this property to in vivo bilirubin glucuronidation. Drug Metab Dispos 25; 33: Gerber JG, Rosenkranz SL, Fichtenbaum CJ, Vega JM, Yang A, Alston BL, Brobst SW, Segal Y, Aberg JA, the AIDS Clinical Trials Group A518 Team. Effect of efavirenz on the pharmacokinetics of simvastatin, atorvastatin, and pravastatin: results of AIDS Clinical Trials Group 518 Study. J Acquir Immune Defic Syndr 25; 39: Fichtenbaum CJ, Gerber JG, Rosenkranz SL, Segal Y, Aberg JA, Blaschke T, Alston B, Fang F, Kosel B, Aweeka F, the NIAID AIDS Clinical Trials Group. Pharmacokinetic interactions between protease inhibitors and statins in HIV seronegative volunteers: ACTG study A547. AIDS 22; 16: Schmidt GA, Hoehns JD, Purcell JL, Friedman RL, Elhawi Y. Severe rhabdomyolysis and acute renal failure secondary to concomitant use of simvastatin, amiodarone, and atazanavir. J Am Board Fam Med 27; 2: Br J Clin Pharmacol / 74:2 / 345